The invention relates generally to adsorption arrangements. More particularly, the invention relates to an adsorption arrangement wherein the adsorbing agent is regenerated or reactivated.
The purification, separation or drying of fluids, especially solvent mixtures, is, in known manner, achieved by sorption of the undesired components or impurities onto microfilters or other adsorption agents such as activated alumina, activated carbon or silica gel. Subsequent to the sorption, the adsorption agent must be reactivated.
The reactivation of the adsorption agent has, in the known methods used until now, usually been carried out by conveying a gaseous substance different from the fluid purified by the adsorption agent through the latter at elevated temperature. The degree of activation achieved or, in other words, the quantity of residual impurities still adhering to the adsorption agent after the reactivation, determines the degree of purity achievable for the fluid to be purified with the adsorption agent.
Organic compounds such as, for example, solvent vapors, have a great tendency to form explosive gas mixtures when they are mixed with air and, in addition, have a great tendency to undergo coking at temperatures in excess of 200.degree. C. The latter effect has the result that tar-like desposits form on the adsorption agent. In view of the above, the reactivation or regeneration of adsorption agents has generally been performed by using nitrogen.
For economic reasons, the nitrogen must be recirculated. During this process, the adsorbate, that is, the impurities adsorbed by the adsorption agent and which are removed therefrom by the nitrogen, are extracted or segregated from the hot nitrogen by cooling. This process exhibits various disadvantages.
Where nitrogen is used as a regenerating medium and Na-A-zeolite is used as an adsorption agent, the conditions for achieving a residual adsorbed water or moisture content of the order of 2% for the adsorption agent are, for instance, as follows:
A. regeneration temperature 350.degree. C Dew point of the inert gas 27.degree. C PA1 B. regeneration temperature 270.degree. C Dew point of the inert gas 2.degree. C PA1 C. regeneration temperature 150.degree. C Dew point of the inert gas -40.degree. C
The regeneration temperature for the microfilter, which latter is used for the purification of solvents, is too high in the Examples A and B given above since, as already mentioned, coking occurs at temperatures in excess of 200.degree. C. On the other hand, the dew point of the recirculated regenerating gas in the Examples B and C above can only be obtained by using heat-exchangers in conjunction with the cooling systems.
Furthermore, since some of the fluid to be purified always remains as a component in the desorbing gas, that is, the gas used for reactivating the adsorption agent, losses are to be expected due to emissions which are very difficult to eliminate. There is also the further consideration that the danger of an explosion is not completely out of the question since the recirculating system can be sealed off only at very high expense.
Therefore, it is desirable to improve on the known methods of regenerating adsorption agents.